This invention relates to novel improved dithiocarbamates that are free of alkali, metal and alkylene thiourea as well as dithiocarbamates that do not form undesired degradation products such as ethylenethiourea (2-imidazolidinethione or ETU). More particularly, this invention relates to di- and trialkyldithiocarbonates that are useful for providing an effective fungicide, insecticide, microbicide and bactericide.
In the past dithiocarbamate compounds, particularly the alkyl esters of dithiocarbamic acid have generally been produced by the reaction of equimolar amounts of mono- or dialkylamine, carbon disulfide and NaOH in the presence of water. The resulting water-soluble products, generally form amber colored liquids, as noted in British Patent Specification No. 805,500, said coloring rendering these materials undesired for application to fruits, vegetables and other agricultural products intended for human consumption because of the discoloring and/or spotting of said products. Thus, the marketability of these products are significantly reduced. In addition, the use of alkali metal hydroxides in the preparation of dithiocarbamates appears to result in the formation of undesired side reaction products, and it is believed that the presence of these side reaction products, which cannot be separated from the dithiocarbamic esters, is believed to be responsible for both the discoloring as well as the environmental hazards associated with dithiocarbamates in the past.
The use of NaOH or KOH in the general reaction results in the formation of the alkali salt which has the general formula: RR'NCSSM wherein M is Na or K. The latter compound is reacted with an alkyl halide which results in the formation of the corresponding alkyl ester of a mono- or dialkyldithiocarbamic acid, said reaction being represented by the following formula: EQU RR'NCSSM+R"X.fwdarw.RR'NCSSR+MX
The two reaction products are both quite difficult to separate from one another due to the tendency of the dithiocarbamate ester to decompose when subjected to temperatures above about 80.degree. C. In this regard, it is noted that the boiling points of the dithiocarbamate esters is on the order of about 200.degree. C. with the sodium halides and potassium halides having melting points considerably higher than 200.degree. C. (except for KF which has a melting point of 41.degree. C.).